So-called automatic darkening filters are often used for applications such as welding, where protection from intense levels of incident light is desired. A typical automatic darkening filter can be controllably changed from a light (relatively transparent) state when not subjected to high intensity light, to a dark (relatively opaque) state upon exposure to such light. Such automatic darkening filters are often constructed from a combination of one or more polarizing layers and one or more liquid crystal cells, aligned in the same optical path.
In a liquid crystal cell, the molecules of liquid crystal material are typically aligned in a preferred direction. This alignment is often accomplished through the use of an alignment layer on each side of the liquid crystal material. Alignment layers are often polymeric films, (e.g. polyimides), that are mechanically rubbed in a single direction to provide an oriented structure that imparts an aligning effect on the liquid crystal material. The alignment of the liquid crystal material can then be altered by the imposition of an electric field, in order to manipulate the optical transmissivity of the cell.
Chromonic materials, when deposited and dried so as to form a highly oriented structure, have found use as alignment layers in liquid crystal cells. Also, pleochroic dyes have been incorporated into chromonic materials, such that the dried and oriented chromonic material may function as a polarizing layer. Thus, chromonic materials with pleochroic dyes therein may provide a single layer that can serve as a combined alignment/polarizer layer.